Transcriptome analysis of Listeria monocytogenes exposed to biocide stress reveals a multi-system response involving cell wall synthesis, sugar uptake, and motility

peer-reviewedListeria monocytogenes is a virulent food-borne pathogen most often associated with the consumption of “ready-to-eat” foods. The organism is a common contaminant of food processing plants where it may persist for extended periods of time. A commonly used approach for the control of Listeria monocytogenes in the processing environment is the application of biocides such as quaternary ammonium compounds. In this study, the transcriptomic response of a persistent strain of L. monocytogenes (strain 6179) on exposure to a sub-lethal concentration of the quaternary ammonium compound benzethonium chloride (BZT) was assessed. Using RNA-Seq, gene expression levels were quantified by sequencing the transcriptome of L. monocytogenes 6179 in the presence (4 ppm) and absence of BZT, and mapping each data set to the sequenced genome of strain 6179. Hundreds of differentially expressed genes were identified, and subsequent analysis suggested that many biological processes such as peptidoglycan biosynthesis, bacterial chemotaxis and motility, and carbohydrate uptake, were involved in the response of L. monocyotogenes to the presence of BZT. The information generated in this study further contributes to our understanding of the response of bacteria to environmental stress. In addition, this study demonstrates the importance of using the bacterium's own genome as a reference when analysing RNA-Seq data.This work was supported by the E.U.7th framework projects PROMISE (project number 265877)and FOODSEG(project number 266061).Aidan Casey was supported by the Teagasc Walsh Fellowship programme

A tail of two phages: genomic and functional analysis of Listeria monocytogenes phages vB_LmoS_188 and vB_LmoS_293 reveal the receptor-binding proteins involved in host specificity

The physical characteristics of bacteriophages establish them as viable candidates for downstream development of pathogen detection assays and biocontrol measures. To utilize phages for such purposes, a detailed knowledge of their host interaction mechanisms is a prerequisite. There is currently a wealth of knowledge available concerning Gram-negative phage-host interaction, but little by comparison for Gram-positive phages and Listeria phages in particular. In this research, the lytic spectrum of two recently isolated Listeria monocytogenes phages (vB_LmoS_188 and vB_LmoS_293) was determined, and the genomic basis for their observed serotype 4b/4e host-specificity was investigated using comparative genomics. The late tail genes of these phages were identified to be highly conserved when compared to other serovar 4-specific Listeria phages. Spontaneous mutants of each of these phages with broadened host specificities were generated. Their late tail gene sequences were compared with their wild-type counterparts resulting in the putative identification of the products of ORF 19 of vB_LmoS_188 and ORF 20 of vB_LmoS_293 as the receptor binding proteins of these phages. The research findings also indicate that conserved baseplate architectures and host interaction mechanisms exist for Listeria siphoviruses with differing host-specificities, and further contribute to the current knowledge of phage-host interactions with regard to Listeria phages